1 E2040 Introduction to Epidemiology and Environmental Health Measures of association and effect β€”Practice Exercises Exercise 1 In their study of the relationship between smoking and lung cancer, Wynder and Graham (1950) identified 100 men with cancer of the lungs (cases) and 186 men who had other chest diseases but no cancer. After identifying these men, the researchers asked them about their lifetime smoking habits. Individuals who smoked pipes or cigars were included in this dataset (1 cigar was equivalent to 5 cigarettes and 1 pipeful as 2.5 cigarettes). The researchers then divided their study participants into 6 categories, as follows: 0 = nonsmokers (less than 1 cigarette per day for over 20 years) 1 = light smokers (1-9 cigarettes per day for more than 20 years) 2 = moderately heavy smokers (10-15 cigarettes per day for more than 20 years) 3 = heavy smokers (16-20 cigarettes per day for more than 20 years) 4 = excessive smokers (21-34 cigarettes per day for more than 20 years) 5 = chain smokers (35+ cigarettes per day for more than 20 years) This type of study is called case-control study (we will learn more about this in the coming weeks), and the disease being observed is prevalent disease. Smoking intensity Cancer status Total Prevalence by smoking intensityCancer No cancer None 0 26 26 Light 5 20 25 Moderately heavy 7 21 28 Heavy 35 76 111 Excessive 30 27 57 Chain 23 16 39 Total 100 186 286 1. Describe the observed prevalence of disease depending on smoking intensity. 2. What level of disease would you expect in these patients? Use the above table to calculate the expected cancer prevalence for each cell. 2 3. Calculate the Ξ§2 statistics to understand if there is an association between cancer status and smoking in the population. 4. Based on the correct DF and a 2-sided alpha of 0.05, would you say that smoking intensity is related or unrelated to lung cancer? 3 Exercise 2 The hypothetical dataset below contains data on 30 adults from Brno who developed bronchitis during the week of October 10, 2023. Information on sex (1=male, 2=female), smoking (0=nonsmoker, 1=smoker) and bronchitis (0=no, 1=yes) is available for each person. Case number Sex Smoking status Bronchitis 1 1 1 0 2 1 1 1 3 2 0 0 4 1 0 0 5 1 1 1 6 2 1 1 7 2 0 0 8 2 0 0 9 2 0 1 10 1 1 1 11 1 0 0 12 1 1 0 13 2 1 0 14 1 0 0 15 2 0 1 16 2 0 0 17 1 1 1 18 1 1 1 19 1 0 0 20 2 0 0 21 2 0 0 22 1 1 0 23 1 1 1 24 1 0 0 25 2 1 1 26 1 0 0 27 1 0 1 28 2 1 0 29 1 1 1 30 2 1 1 1. What is the prevalence of smoking in this sample: a. Overall? b. In men and women separately? 2. Create the following 2x2 tables: a. Bronchitis incidence by sex b. Bronchitis incidence by smoking status 4 3. Calculate the following: a. Incidence of bronchitis in men and women b. Incidence of bronchitis in smokers and non-smokers 4. Do you think the incidence of bronchitis is different among smokers vs. non-smokers? a. State your null and alternative hypothesis about this relationship. b. Select a test of statistical significance to carry out your hypothesis test. c. Perform the calculations. d. Interpret the results and state your conclusions. 5 Exercise 3 One study followed 3,600 employees of London Underground for 20 years. The employees completed a smoking questionnaire at the start of the study and investigators tracked the incidence of lung cancer throughout the duration of the study. Lung cancer No cancer Total Smoker 300 1000 Non-smoker 100 2200 Total a. Complete all parts of the table above. Calculate the absolute risk of developing lung cancer among smokers and non-smokers, as well as overall. b. Calculate the relative risk (RR) of lung cancer by smoking status. Interpret the RR, assuming that it is statistically significant (its 95% CI does not cross 1). c. What do you conclude from your calculations? Which statistics is more informative with respect to the impact of smoking on lung cancer risk in the population? Explain your answer. 6 Exercise 4 In a study of 1000 retired policemen in Austria, researchers tracked the development of liver cancer over a 25-year period. Half of the policemen consumed alcohol regularly during their retirement and 20 cases of liver cancer occurred in this group. In the rest of the study population, 10 cases were diagnosed. a. Create a table to illustrate the data from this study. What was the incidence of cancer in each group? Alcohol consumption Liver cancer No cancer Total Incidence Regular consumer Non-consumer Total b. What is the relative risk of liver cancer among regular consumers vs. non-consumers of alcohol? c. Calculate the odds ratio for the same association. What do you conclude from the results of (b) and (c)? d. What other information would you like to have about these individuals to better understand the relationship between drinking and risk of liver cancer? List the variables/type of information you wish were available and explain how it might be a risk factor for liver cancer. 7 Exercise 5 Ignac Semmelweis (1818-1865) began his medical career in 1844 in obstetrics and midwifery at the Vienna General Hospital (Allgemeines Krankenhaus). There were two maternity wards (divisions) in the hospital: patients in the first division were examined by doctors and medical students, while midwives cared for patients in the second division. Semmelweis noticed that there were more maternal deaths in the first division than in the second. In this exercise, you will follow Semmelweis' steps in investigating a problem. Table 1 below lists Semmelweis' first observations. a. Calculate the maternal mortality rate for each year and overall for the two maternity wards. Complete the table above. Maternal mortality rate = (π‘›π‘’π‘šπ‘π‘’π‘Ÿ π‘œπ‘“ π‘šπ‘Žπ‘‘π‘’π‘Ÿπ‘›π‘Žπ‘™ π‘‘π‘’π‘Žπ‘‘β„Žπ‘  π‘›π‘’π‘šπ‘π‘’π‘Ÿ π‘œπ‘“ 𝑙𝑖𝑣𝑒 π‘π‘–π‘Ÿπ‘‘β„Žπ‘ β„ ) x 100,000 b. Do you agree with the conclusion Semmelweis reached that there were more deaths in the first division? c. Is it necessary to calculate the death rate in each year to compare the two divisions? Semmelweiss observed that the medical students and doctors who attended the births often did so soon after performing autopsies on deceased patients. On the other hand, the midwives were not involved in performing any autopsies. Based on this observation, Semmelweiss recommended that the medical students and doctors clean their hands with a chlorine solution after performing an autopsy. This measure began in May of 1847 and again, Semmelweiss recorded the number of maternal deaths. Table 2 below shows maternal deaths before and after the intervention. 8 d. Calculate maternal mortality rates for each period prior to and after the intervention. Complete the above table. e. Was the implemented intervention successful? How would you test this hypothesis? f. Briefly comment on the significance and implications of this research from the point of view of epidemiology and clinical practice.